The present invention relates to a process and an apparatus for the load-dependent control of a hydraulic drive for a compressor arranged at an internal-combustion engine.
On the basis of German Published Unexamined Patent Application No. 3,320,827, it is known to act upon a hydraulic motor by means of a hydraulic pump driven by an internal-combustion engine, this hydraulic motor, in turn, continuously driving a compressor for the supercharging of the internal-combustion engine. The above-mentioned patent text does not contain any information on how a hydraulic drive must be designed and how it must be controlled so that an optimal supercharging exists in any load range while utilizing the kinetic energy of the exhaust gases of the internal-combustion engine.
The present invention, therefore, has an objective of providing a process for the load-dependent control of a hydraulic drive, by which even during the idling of the internal-combustion engine, a relatively high compressor speed can be obtained, and in positive load changing, an optimal torque is available for the high-speed acceleration of the compressor. Nevertheless, the additional fuel consumption that must be accepted because of the work for the hydraulic drive to be carried out by the internal combustion engine, is kept to a minimum by this process.
This and other objectives are achieved in a process for the load-dependent control of a hydraulic drive for a compressor arranged on an internal combustion engine by providing a process comprising adjusting a hydraulic pump into a full delivery position during idling of the internal combustion engine. The process also includes guiding the hydraulic pump from the full-delivery position to a zero-delivery position according to predetermined characteristics after a positive load change of the internal combustion engine from idling and after a predetermined hydraulic pump control pressure in a hydraulic pipe connecting the hydraulic pump and the hydraulic motor is reached. The hydraulic drive is disconnected after a predetermined charging pressure limit is reached.
In an alternate embodiment of the process, the hydraulic pump is adjusted into a full-delivery position and the hydraulic motor into a minimum intake position during idling of the engine. The hydraulic motor is guided from the minimum intake position to a maximum intake position and the hydraulic pump is kept in a full-delivery position after a positive load change of the engine from idling and when a predetermined hydraulic motor control pressure in the hydraulic pipe is reached. The hydraulic pump is guided according to predetermined characteristics from the full-delivery position to a zero-delivery position after a predetermined hydraulic pump control pressure is reached in the hydraulic pipe. The hydraulic drive is disconnected from the compressor after a predetermined charging pressure limit is reached.
Due to the fact that the hydraulic pump is in the full-delivery position as early as during the idling of the internal-combustion engine, a high compressor speed can therefore be obtained as early as during idling. The high compressor speed is achievable by means of a pump of relatively small dimensions if a hydraulic motor is used having an adjustable working volume and if this motor is in the minimum position during the idling of the internal-combustion engine. A high compressor speed during idling means that in this operating condition, a relatively high supercharging pressure exists in the charge air pipe in the internal-combustion engine.
If now a positive load change takes place, the internal-combustion engine speed increases immediately which results in an immediate rising of the delivery flow of the hydraulic pump. However, an increased delivery flow also at the same time results in an increase of the torque made available by the hydraulic motor in order to increase the compressor acceleration. This effect, in turn, is also achieved by a hydraulic pump with small dimensions while using an adjustable hydraulic motor, if its capacity in the case of a positive load change is brought into the maximum position which results in an increase of the throughflow of hydraulic fluid through the hydraulic motor per revolution. As a result, the torque offer of the hydraulic motor increases in order to overcome the forces of inertia of the compressor, of the compressor shaft and of the exhaust gas turbine arranged in the exhaust gas pipe of the internal-combustion engine.
Based on the compressor speed that previously was relatively high during idling anyway, the compressor therefore, when changing from idling into the load range of the internal-combustion engine, exhibits an optimal acceleration behavior, whereby the so-called "turbo-hole", which is the time period until the compressor is at a speed that is required for a good supercharging, is reduced to a minimum. When the required compressor speed or the indicated loading pressure limit is reached i.e., when the exhaust gas turbine furnishes the required power for the further acceleration of the compressor, the hydraulic drive is disconnected from the compressor. The hydraulic pump, in this embodiment, can be moved back to its zero delivery capacity or minimum delivery capacity. As a result, the additional fuel consumption of the internal-combustion engine that is necessary for the work required for the hydraulic drive is kept to a minimum. The adjusting of the hydraulic pump from the full-delivery position in the direction of the zero-delivery position that the permissible pressure in the hydraulic pipe is not exceeded, has the advantage that the pump driving power can be reduced to a minimum because of the elimination of the delivery of the excess amount that flows off in an unutilized way at the pressure relief valve.
An arrangement for carrying out the process described above includes turbine means connected to drive train means for transmitting torque to the compressor, this turbine being acted upon by exhaust gas flow in an exhaust gas pipe of the internal combustion engine. The drive train means includes, between the compressor and a hydraulic motor, transmission gearing means having one way clutch means that starts to operate when a charging pressure limit is reached. The hydraulic motor has a constant intake volume, and the hydraulic pump includes means for controlling its delivery volume.
In another preferred embodiment, the intake volume of the hydraulic motor is adjustable as a function of the pressure in the hydraulic pipe connecting the hydraulic pump and the hydraulic motor.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.